Cathode structure



y 25, 1943- D. F. DRIE'SCHMAN 2,442,163

CATHODE STRUCTURE Original Filed Aug. 31, 1943 2 Sheets-Sheet 1 H15 ATTORNEY y 1948- D. F. DRIESCHMAN 2,442,163

GATHODE STRUCTURE Original Filed Aug. 51, 1945 2 Sheets-Sheet 2 Dona/J E flr/esc an BY M5 Hi5 ATTOR NE Y Patented May 25, 1948 CATHODE STRUCTURE Donald F. Drieschman,

signor to Eitel-McCullough, Inc.,

San Carlos, Calif-Z, as-

San Bruno,

Calif, a corporation of California,

Original application August 31, 1943, Serial No.

Divided and this application September 1, 1944, Serial No. 552,310

d of fabricating a cathode structure of the character described.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description f my invention. It is to be understood that I do not limit myself to this disclosure of species of my invention as I may adopt variant embodiments thereof within the scopeof the claims.

Referring to the drawings:

Figure 1 is an elev-ational view of a cathode structure embodying the improvements of my invention; and

Figure 2 is an enlarged detail sectional view taken in a plane indicated by line 2-2 of Figure 1, showing the welded joint and special alloy formed at the weld.

Figure 3 is an exploded vertical sectional view of the cathode and assembly jig.

Figure 4 is a vertical sectional View of a cathode in a bell jar ready for arc welding.

Figure 5 is a plan view of a modified arrangement for welding, using a high frequency coil.

In terms of broad inclusion, my cathode structure comprises a plurality of filament wires welded at opposite ends to metallic supports by a metallic welding material. The material used to make the weld comprises a refractory metal, such as columbium or tantalum, and preferably includes a minor proportion of another metal, such as ruthenium. One of the supports is movable, and means associated with the movable support is provided for tensioning the filament wires. An improved method is also provided for holding the filament wires and supports in assembled relation during the welding operation.

In greater detail, and referring to the drawings, my improvements are illustrated in conjuno tion with an electrode for a vacuum tube, and more particularly to a cathode structure. As shown in Figures 1 and 2, the cathode comprises a multiplicity of say 40 parallel wires 2 of thoriated tungsten divided into four groups disposed in cylindrical formation about the cathode axis, each group of wires being connected at the lower 2 end to one of the four tungsten cathode leads 3 and all being connected at the upper end to a common terminal 4.

Fixed supports for the lower ends'of the filament wires are provided by brackets 6 welded to the leads and to quadrant sections 1 having arcuate rims to which the groups of filament wires are welded. Leads 3 are sealed in a four-way press 8 on a suitable stem 9 of glass or the like. The upper support or terminal 4 is a cap having a circular rim to which the upper ends of the filament wires are welded. These upper and lower supports are of a refractory metal such as tantalum 0r molybdenum, tantalum being preferred.

Top cap 4 provides a movable support and is held centered by a tungsten rod or standard ll sealed to the stem and projecting through the cap, Tension is uniformly applied to all the filament wires by a sleeve [2 slidable along the center rod and urged upwardly against cap 4 by a spring [3 interposed between the sleeve and stem.

In the final tube diametrically opposed cathode leads 3 are connected in parallel to a source of heating current.. Since two of the groups of-filament wires are connected in series with one pair of leads and the other two groups are connected in series with the other two leads, all of the filament wires are simultaneously heated. This structure has the advantage of compacting a multiplicity of filament wires in a relatively small cirole, whereby a large amount of electron emitting surface is made available.

The main problem in fabricating such a structure is of course securing the ends of the filament wires to the supporting members. Ordinary spot welding'practice is not feasible because of the close spacing between the wires. I have solved the problem by a special material and welding technique, resulting in the formation of a bonding medium or layer [4 in which the filaments are embedded. See Figure 2. This layer preferably comprises an alloy composed of a major proportion of columbium and a minor proportion of ruthenium, the preferred proportions being about 4% to 20% by weight of ruthenium and the balance columbium. Other refractory metals such as tantalum may be substituted in whole or in part for the columbium component of the alloy. Likewise other metals ingroup 8 of the periodic table may be substituted for the ruthenium com ponent. However the columbium-ruthenium composition is superior in many respects and is preferred. This alloy has a high melting point, low vapor pressure, is very hard and makes an thefbllf jar. Rotation excellent bond between refractory metals such as tungsten and the like. These properties make the alloy especially suited for a joint structure in a cathode where exceedingly high temperatures are involved.., p

The preferred method of making; the cathode utilizes a. jig (Figure 3)' comprising a cylindrical core [6 of say copper having longitudinal grooves in the surface to receive filament wires 2, thelatter being straight, rod-like pieces cut to size.-

These wires are temporarily held b a rubber band l1; core I6 being proportioned so thatw-ires- 2 project freely from the ends.

6 are formed as a one-piece ring. 18 which is At this stage 7 of fabrication the quadrant sections on brackets later severed at four places to' make. the. in-

bonding allo-yat'thewe1d comprises. .a'mixture of finelydivided particles or 'columbium and ruthenium. The columbium particles should not be" larger thaniabout 200" mesh, a particlesize of 400 mesh being preferred: The rutheb i flniumparticles used are preferably still; more finely di-vided, a powder known commercially as ruthenium black being preferre'd. These;1particlesaremiiiedtogether, with a liquid vehicle;

such asw ater, toa thin pasty consistencysuitable .for; application with a brush. This material is then brushed onto the over end portions shownat 5 151 Figure 4; V

With the material applied the assembled cathode is their elevated-in bell jar' Eli-to position rims ofth'e supports and the upper support nest an electric :arc'discharging between l'electrodes': 2i sealed to the sides of V Of'the cathode by the operatoiiexposes successive portions of the rim to the intense heatlof the are; the top weld the structure is moved upto weld the filaments-at the lower support. A non-oxie and to give uniform spreading dizirig atmospherefis maintained in; thebell jar by admittingagas, such'as hydrogen, through asuitable duct 22. p V v In making these welds'I find that the material 7 melts and flows out-uniformly land-smoothly over thejoint? The ruthenium performs animportant function at this stage, serving as a wetting agent U 7 p V of the material over the'surfaces The final' composition formed by the 'coI-umbiu-m and ruthenium is a hard; tough alloy having good bond ing afiinity for'other refractorymetals such as the tungsten filaments 2 and tantalum supports {and :8. ,These prop: ertiesjinsur strong mechanical joints at the ends of ithefilfaments. Furtherm'ore thehi'gh melting point and low va or pressure of the bonding'mediam producesa; weldwhich will readilywith stand the incandescent operating temperatures of the filamentwires. g

Instead "of using an arc the heat required for making the weld may be supplied-by high fre quency induction, using a coil 23' as shown in of the filament. wires as Figure 5; this coil being positioned in a suitable bell jar so that the non-oxidizing atmosphere.

may be supplied. The assembled cathode on the jig is elevated to place the desired portions of the cathode within thecoiLwhereupon the coil is energized to induce the. required amount of heat. Since lowersupport 13'' is a continuous ring at I this time the induction heating method may be used at the bottom as well as at the top welds. After the welds are completed ring it of the lower support is cut in four places between brackets G to separate it into the quadrant sections 5;

Show irl-F g e 1. J core I6 is thenremoved by spreading the lower end of the cathode. The cathodeis now ready for final mounting, to-

gather' with .the spring tensioning device, on'

stem 9 I claim:

I. A cathode structure comprising spaced supports of refractory metal,'tungsten filament wires secured to said supports by a'metalli'o welding material, the meta-1i of saidmaterial consisting essentially of an alloy of columbiuzn no 4% to-20-% of ruthenium.

After finishing 2. A cathode structure comprising spaced sup; ports of reiractorymetal, and tungsten filament wires secured to said supports by a metallic weld- @3 1 ing essentially of an alloy of refractory metal ing material, the metal of said material selected from the'group consisting of coIuInb'i u-m and tantalum with a minor nium.

wires secured to said supports by a metallic welding material; the metal" of said material consisting essentially of an alloy of refractory metal'selected from the group consisting oi'columbiumandtam1 talum withfrom4%'to 2il-%"of:ruthenium. 7 V 4. An electrode structure comprisingmembers of refractory metal secured together by a metallic welding material; the metalof said material consisting essentiallyof an alloy of a refractorymet al' selected" from the group consisting of columbium' REFERENCES orrun The following reference file of this patent; 7

UNIIED: STATES, PATENTS Date Number Name 7 V 7 Re. 13,961 Zimmerman Aug, 10, 1915 991,578 Whitney May 9-, 1911 1,115,426 Liebman Oct. 5, 1915 1,389,351 Harvey -1; Aug. 30,1921 1,730,003 Goldsmith et al. Oct.'1 1929; 1,807,885 Weingartner June 2, 1931 2,072,676 Jedele j Mar. 2, 1937' 2,075,639 5 Castle Mar. 30,1937 2,097,178 de'Golyer 10ct. 26; 1937 2,188,636 Vilensky Jan. 30, 1946 2,225,853 Baker "11sec. 24,1946 2,298,929 Dailey Oct. "13; 1942' 2,341,716 Herdman Feb'. 15, 1944 2,350,270 Atlee May 3, 1944 FOREIGN. PATENTS Number Country Date 528,688 Germany July 2, 1931' proportion of ruthef 3-. A cathodestructurecomprising spacedsup- 1 ports of'refractorym'etal; and tungsten filament s are. oiirec'ord the 

